More than 40,000 people from Britain and abroad stood shoulder to shoulder outside the gates of Buckingham Palace to honor the country’s favorite grandmother, Queen Mother Elizabeth, on her 100th birthday yesterday.

There was a roar when the Queen Mum, a small, frail figure in blue silk, stepped onto the palace’s balcony with her two daughters, Queen Elizabeth and younger sister Margaret.

She was joined by her grandchildren and great grandchildren – a total of 27 royals in all – and the crowd broke into a spontaneous chorus of “Happy Birthday to You.”

The outpouring of joy recalled the emotional day in 1945 when the Queen Mother and her late husband, King George VI, stepped out onto the same balcony to mark the end of World War II.

“I think I’m going to cry,” said Judy Crook, 41, who was among the thousands outside the palace. “I think the Queen Mother is lovely. She’s very regal, just like a queen mum should be.”

Betsy Pelling, 59, agreed, saying, “I’ve liked her since 1947 when I saw her as a little girl. I live in South Africa, but I made sure I was here for this.”

The day began when the Queen Mother took the salute from a troop of mounted soldiers outside her Clarence House residence.

Postman Tony Nichols, 58, then hand-delivered a special birthday card from Queen Elizabeth. It was signed “Lilibet” – the 74-year-old queen’s childhood nickname.

The Queen Mother then drove to Buckingham Palace with her grandson, Prince Charles, in an open landau pulled by four white horses and bedecked with blue and yellow flowers.